It's bad before the wort is below about 85F. It's good after that and up to about 12 hours (or so) after fermentation starts. It's generally bad after that. So the best period for aeration is after the wort is below 85F and before it's 12 hours into fermentation.

Welcome to the forum, Kyle! There are great brewers who can answer your questions and you can also search a lot of topics that have been pretty well settled by discussion.

Denny - with using a WIC do you find that the wort is aerated slightly by the whirlpooling against the immersion chiller? With mine I get a slight burp as I start it, from air in the hoses, then it is just mixing wort. That can't be much of a problem, right?

According to Bamforth, any aeration while hot is going to be cleaned up in a healthy fermentation. Unless you are aerating to the point that it's using up all of your head forming materials, but then you just won't have much head.

Before I heard about hot side aeration I used a mix stir to aid my chiller. My experience is that the final beer has no oxidation and the head retention was minimally effected.

According to Bamforth, any aeration while hot is going to be cleaned up in a healthy fermentation. Unless you are aerating to the point that it's using up all of your head forming materials, but then you just won't have much head.

Before I heard about hot side aeration I used a mix stir to aid my chiller. My experience is that the final beer has no oxidation and the head retention was minimally effected.

In his most recent BeerSmith interview, he went a bit short of saying that there is no such thing as HSA. What he did emphasize, firmly and repeatedly, is that it's a waste of time to worry about the effects of HSA until you shore up all your practices downstream.

He did say that once you have your fermentation, packaging and storage practices tightened up, then you may possibly see some benefit to minimizing O2 on the hot side. So, not exactly a ringing endorsement of the spectre of HSA. And to your point, he also mentioned that yeast do a good job at mopping up a lot of the off flavors that may be produced prior to fermentation.

Denny - with using a WIC do you find that the wort is aerated slightly by the whirlpooling against the immersion chiller? With mine I get a slight burp as I start it, from air in the hoses, then it is just mixing wort. That can't be much of a problem, right?

Maybe a bit, but it's never caused a problem. My point of view is to be conservative...there's little danger IMO, but it's so easy to avoid that there's no reason not to.